Propeller fan, and air blower, air conditioner, and hot-water supply outdoor unit including the same

ABSTRACT

In a blade cross-sectional view, assuming that a tangent at an end of the outer periphery is defined as LQ, an imaginary line orthogonal to the rotation axis is defined as LO, an angle formed by the tangent (LQ) and the imaginary line (LO) is defined as an outer peripheral end tangent angle (θ), and a position at which an imaginary plane including a position of an intake-side end portion of the bellmouth and a peripheral edge of the blade cross each other is defined as an overlap starting point, the outer peripheral end tangent angle on a trailing edge portion side with respect to a blade cross section including the overlap starting point is set to be smaller than the outer peripheral end tangent angle on a leading edge portion side with respect to the blade cross section including the overlap starting point.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application ofPCT/JP2013/069505 filed on Jul. 18, 2013, which claims priority tointernational application no. PCT/JP2012/070507 filed on Aug. 10, 2012,the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a propeller fan, and an air blower, anair conditioner, and a hot-water supply outdoor unit including thepropeller fan.

BACKGROUND ART

As propeller fans to be used in air conditioners and the like, PatentLiterature 1 discloses such a propeller fan that a part of the propellerfan on an outer peripheral side thereof is formed into a concave arcshape in a blade cross section, and the radius of curvature of the arcis increased as approaching from a leading edge to a trailing edge so asto suppress generation of a blade tip vortex caused by a leakage flowdirected from a leeward side to a windward side.

Further, Patent Literature 2 discloses such a configuration that a forceapplied from a blade to air is directed inwardly by tilting the blade toa downstream side as approaching toward a trailing edge so that air blowspeed is made uniform to suppress noise.

CITATION LIST Patent Literature

[PTL 1] JP 2003-148395 A (FIGS. 1 and 3)

[PTL 2] JP 06-229398 A (FIGS. 1 and 8)

SUMMARY OF INVENTION Technical Problem

In the air blowers, there is a demand for both increase in air-blowingrate (rate of air to be blown) and reduction in noise. In this case,first, regarding the noise, when a flow, which leaks from an outerperipheral portion of a blade, occurs, there may cause problems in thatthe disturbance increases due to the generation of a blade tip vortex,and the noise also increases. On the other hand, when the blade is tiledinwardly so as to suppress the flow leaking from the outer peripheralportion of the blade, there may arise a problem in that the surface ofthe blade is directed inwardly in the fan, and an axial componentbecomes insufficient among force components applied to an air current bythe fan, thereby decreasing the rate of air to be blown.

Regarding those problems, in the above-mentioned configuration of PatentLiterature 1, there is a risk in that the blade tip vortex generatedfrom the outer peripheral portion of the blade interferes with abellmouth while flowing to the downstream side, thereby increasingnoise. Specifically, the bellmouth is set on an outer peripheral side ofthe propeller fan used in air conditioners, and the clearance betweenthe bellmouth and the outer periphery of the fan is generally as narrowas about 5 mm to about 10 mm so that noise may increase when a disturbedair current impinges against the bellmouth. Further, the loss of energyis also caused due to the friction resistance generated between theswirling air current and the bellmouth.

On the other hand, in the configuration of Patent Literature 2, the flowleaking from the outer peripheral portion of the blade can be reduced byinwardly directing the force applied from the blade to the air current.However, there is a problem in that the axial force component becomessmall at an exit (trailing edge) of the blade, and the air-blowing ratewith respect to the number of rotations therefore decreases, with theresult that the energy required for air blowing increases. That is, inthe configuration of Patent Literature 2, the suppression of the leakagecan be expected to some degree, but it is considered to be ratherdifficult to increase the air-blowing rate.

In view of the above-mentioned circumstances, it is an object of thepresent invention to provide a propeller fan capable of achieving lowernoise by suppressing the leakage flow of an air current, and alsoachieving higher efficiency by increasing the rate of air to be blown.

Solution to Problem

In order to achieve the above-mentioned object, according to oneembodiment of the present invention, there is provided a propeller fan,including: a boss including a rotation axis; a plurality of bladesformed on an outer periphery of the boss; and a bellmouth arranged so asto surround the plurality of blades at a trailing edge side of each ofthe blades. The blade has a bending portion that bulges toward anupstream side in a cross-sectional shape in a radial direction. In ablade cross-sectional view, assuming that a tangent at an end of theouter periphery is defined as LQ, an imaginary line orthogonal to therotation axis O is defined as LO, an angle formed by the tangent LQ andthe imaginary line LO is defined as an outer peripheral end tangentangle θ, and a position at which an imaginary plane including a positionof an intake-side end portion of the bellmouth and a peripheral edge ofthe blade cross each other is defined as an overlap starting point, theouter peripheral end tangent angle θ on a trailing edge portion sidewith respect to a blade cross section including the overlap startingpoint is set to be smaller than the outer peripheral end tangent angle θon a leading edge portion side with respect to the blade cross sectionincluding the overlap starting point.

Advantageous Effects of Invention

According to the propeller fan of the present invention, it is possibleto achieve lower noise by suppressing the leakage flow of the aircurrent, and to achieve higher efficiency by increasing the rate of airto be blown.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a propeller fan according to a firstembodiment of the present invention when seen from a downstream side.

FIG. 2 is a view of the propeller fan of FIG. 1 when seen from a lateralside.

FIG. 3 is a view of the propeller fan of FIG. 1 when seen from adirection of a rotation axis.

FIG. 4 is a radial sectional view taken along the line IV-IV of FIG. 3.

FIG. 5 are radial sectional views of the vicinity of a leading edge of ablade of the propeller fan.

FIG. 6 are radial sectional views illustrating a backward side withrespect to FIG. 5 in the same manner as that of FIG. 5.

FIG. 7 are radial sectional views of the vicinity of a trailing edge ofthe blade of the propeller fan.

FIG. 8 is a view illustrating a relationship between an outer peripheralend tangent angle θ and a point T at a position from a leading edge to atrailing edge according to a second embodiment of the present invention.

FIG. 9 is a view illustrating cross sections of a blade at T0, T1, T2,and T3.

FIG. 10 are views illustrating a state of a flow leaking to an outerside and an inner side in the vicinity of the leading edge of the blade.

FIG. 11 is a view illustrating a third embodiment of the presentinvention in the same manner as that of FIG. 8.

FIG. 12 is a view illustrating the third embodiment of the presentinvention in the same manner as that of FIG. 9.

FIG. 13 is a radial sectional view of a blade of a propeller fanaccording to a fourth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, a propeller fan according to embodiments of the present inventionis described with reference to the accompanying drawings. Note that, inthe drawings, the same reference symbols represent the same orcorresponding parts.

First Embodiment

FIG. 1 is a perspective view of a propeller fan according to a firstembodiment of the present invention when seen from a downstream side. Ina propeller fan 1, a plurality of blades 3 are arranged around a boss 2set at a rotation axis O. The arrow denoted by reference symbol 4indicates a rotation direction. A peripheral edge of each of the blades3 includes a leading edge 5 positioned on a forward side in the rotationdirection, a trailing edge 6 positioned on an opposite side of theleading edge 5, and an outer side edge 7 positioned on a radially outerside so as to connect the leading edge 5 and the trailing edge 6 to eachother. Further, the arrow denoted by reference symbol 8 indicates an aircurrent direction.

FIG. 2 is a view of the propeller fan of FIG. 1 when seen from a lateralside. In FIG. 2, the propeller fan 1 is illustrated so that a rotationlocus is projected on a surface including the rotation axis O. As isunderstood from FIG. 2, the propeller fan 1 is arranged so as to besurrounded by an annular bellmouth 9 from outside in the radialdirection. A predetermined clearance is secured between the propellerfan 1 and the bellmouth 9.

An upstream side A and a downstream side B of the propeller fan 1 arepartitioned by the bellmouth 9. Further, as illustrated in FIG. 2, thepropeller fan 1 also includes a region not surrounded by the bellmouth9. Assuming that an imaginary plane 10 a has the rotation axis O as anormal to the imaginary plane 10 a and includes a position of anintake-side end portion 9 a of the bellmouth 9, a position where theimaginary plane 10 a and the peripheral edge of the blade 3 cross eachother is referred to as an overlap starting point 10 in the description.In FIG. 2, a region of each of the blades 3 on the upstream side withrespect to the overlap starting point 10 is not surrounded by thebellmouth 9 and is kept open in a space on the upstream side A.

FIG. 3 is a view of the propeller fan when seen from a direction of therotation axis, and FIG. 4 is a radial sectional view taken along theline IV-IV of FIG. 3. In each of the blades 3, a blade surface on thedownstream side with respect to the air current direction serves to pushan air current by the rotation of the fan and is referred to as apressure surface 11 or a positive pressure surface, and a blade surfaceon the upstream side with respect to the air current direction isreferred to, on the other hand, as a negative pressure surface 12.

As illustrated in FIG. 4, each of the blades 3 has a bending portion 13that bulges toward the upstream side of a blade cross section, that is,on the negative pressure surface 12 side. An apex of the bending portion13 is defined as “P”. Further, an outer peripheral end of the blade onthe radially outer side with respect to the apex P when seen in theblade cross section is defined as “Q”. Then, a tangent on the outerperipheral end Q of the blade is defined as “LQ”, and an imaginary lineorthogonal to the rotation axis O when seen in the blade cross sectionis defined as “LO”. An angle formed by the two lines LQ and LO isdefined as an outer peripheral end tangent angle θ. When an intersectionbetween the tangent LQ and the imaginary line LO is defined as “IP” inthe drawing sheet of FIG. 4, the outer peripheral end tangent angle θ isan angle formed by a part of the imaginary line LO on an outerperipheral side with respect to the intersection IP and a part of a linesegment of the tangent LQ in a range between the outer peripheral end Qof the blade and the intersection IP.

In the case where the outer peripheral end tangent angle in a leadingedge portion is compared to that in a trailing edge portion under theabove-mentioned presumption, one of the features of this embodimentresides in that the outer peripheral end tangent angle θ in the trailingedge portion is smaller than that in the leading edge portion, that is,the outer peripheral end tangent angle θ becomes smaller toward thetrailing edge portion. Further, regarding the relationship with thebellmouth, one of the features of this embodiment resides in that, whena position of the blade cross section including the above-mentionedoverlap starting point 10 is defined as a corresponding point of theoverlap starting point, the outer peripheral and tangent angle θ on thetrailing edge portion side with respect to the corresponding point ofthe overlap starting point is smaller than the outer peripheral endtangent angle θ on the leading edge portion side with respect to thecorresponding point of the overlap starting point. In an example of thisembodiment, the diameter of the boss is about 30% of the diameter of thefan, and the apex P of the bending portion 13 is set at a position awayfrom the rotation axis O by about 60% or more of the radius so as toserve to suppress a flow leaking from the outer periphery of the blade.Further, when a base of the blade cross section on the negative pressuresurface 12 side is compared to the outer peripheral end Q of the blade,the outer peripheral end of the blade serves as a swept blade mounted onthe downstream side.

Now, the definition of the cross section in the radial direction isdescribed. FIG. 5(b) illustrates a cross section in a radial directiontaken along the line V-V of FIG. 5 (a). The leading edge of the bladehas, in most cases, a shape that extends further forward in the rotationdirection toward the outer periphery side, and as illustrated in FIG.5(a), the entire cross section from the boss to the outer peripheraledge may not appear in the cross section in the radial directionconnecting the rotation center to the leading edge. The apex of thebending portion is set at a position away from the rotation axis O byabout 60% or more of the radius as described above, and hence across-sectional shape is considered within a range in which the bladecross section on an outer side of from about 50% to about 90% of aradius Ro of the fan appears. Specifically, the “leading edge portion”and the “trailing edge portion” as used herein respectively refer to across section on the most leading edge side and a cross section on themost trailing edge side in the range in which the blade cross sectionappears as described above.

Now, the function and the operation of the blade according to thisembodiment are described with reference to FIGS. 6 and 7. FIGS. 6 and 7are views illustrating the blade in the same manner as that of FIG. 5.FIGS. 6(b) and 7(b) illustrate cross sections in a radial directionrespectively taken along the lines VI-VI and VII-VII of FIGS. 6(a) and7(a) corresponding thereto. Further, FIG. 6 illustrate a position on abackward side in the rotation direction with respect to FIG. 5, and FIG.7 illustrate a position on a further backward side in the rotationdirection with respect to FIG. 6.

At the leading edge side that is the outer side of the bellmouth (FIG.6), an outer peripheral end tangent angle θa is large, and a normal tothe blade surface on the outer peripheral side with respect to thebending portion is directed to the inner peripheral side (rotation axisside). Therefore, when the air current flowing onto the pressure surface11 passes by the bending portion 13, a force 14 a applied from the bladeto the air current works at the inner side. As a result, an air current8 in in the vicinity of the leading edge is gathered toward the rotationaxis of the fan, and thus a large amount of air current is supplied tothe downstream side, that is, the increase in air-blowing rate isachieved. Further, the normal to the blade surface is directed to theinner peripheral side, and thus an air current 8 a flows along the bladesurface without leaking from the outer periphery of the blade so thatenergy is supplied to the air current from the blade. Further, theleakage flow hardly occurs, and hence a vortex generated at an end ofthe blade can be suppressed, and noise can be reduced with thedisturbance of the flow being suppressed. Further, the air current 8 ingathered as described above joins the air current 8 a flowing along theblade surface without leaking from the outer periphery of the blade, andthus a larger amount of air current is supplied to the downstream side.Also with this, the air-blowing rate can be further increased.

On the other hand, at the trailing edge side that is the inner side ofthe bellmouth (FIG. 7), an outer peripheral end tangent angle θb issmaller than the above-mentioned angle θa on the leading edge side, andthe normal to the blade surface of the bending portion 13 is directed inthe axial direction compared to the leading edge side. Therefore, theair current receives a force 14 b in the axial direction. As a result, aflow 8 b of the air current, which has flowed on the blade surface toincrease in energy, is pushed out to the downstream side from the bladesurface. In this case, the trailing edge side is surrounded by thebellmouth. Therefore, when the air current is retained between theblades of the fan, there is a risk in that the friction between thebellmouth and the air current may increase to cause the loss of energyand the noise may increase due to the disturbance. However, in thisembodiment, the friction is suppressed on the trailing edge side byrapidly discharging the air current in the overlapping region betweenthe trailing edge side and the bellmouth in the axial direction. Withsuch a process, lower noise is achieved by suppressing the generation ofa vortex and the friction, and the increase in air-blowing rate is alsoachieved by actively pushing out the flow to the downstream side whiletaking in the air current in a manner of gathering the air current andsuppressing the friction and leakage.

According to this embodiment configured as described above, in theleading edge portion on the intake side, the air current flowing on thepressure surface is prevented from leaking to the outer periphery withthe bending portion that bulges toward the upstream side so that the aircurrent is allowed to flow along the blade surface so as to be suppliedwith energy. In addition, the angle of the bending portion is set to begentler toward the trailing edge portion, and the direction of thenormal to the blade surface is directed in the axial direction so thatthe air-blowing rate can be increased while the loss of energy caused bythe friction between the air current and bellmouth is suppressed.Further, the leakage flow is suppressed, and hence the disturbance ofthe air current is suppressed so as to reduce the noise.

Second Embodiment

Next, a second embodiment of the present invention is described withreference to FIGS. 8 and 9. FIG. 8 is a view illustrating a relationshipbetween an outer peripheral end tangent angle θ and each point T at aposition from a leading edge to a trailing edge according to the secondembodiment. FIG. 9 is a view illustrating cross sections of a blade atT0, T1, T2, and T3.

As illustrated in FIG. 8, in a propeller fan 101 according to the secondembodiment, the outer peripheral end tangent angle θ takes a constantvalue up to the point T1 located between the leading edge portion T0 andthe trailing edge portion T3 and then decreases from the point T1 to thetrailing edge portion T3. In the illustrated example of FIG. 8, theouter peripheral end tangent angle θ decreases linearly.

Further, in the blade cross sections of FIG. 9, the outer peripheral endtangent angle θ is constant as indicated by θ1 in the blade crosssections at the leading edge portion T0 and the point T1, and the outerperipheral end tangent angle θ decreases to an angle θ2 and an angle θ3respectively from the point T1 to the points T2 and T3.

In this case, a chord length of the propeller fan is longest on theouter peripheral side, and as illustrated in FIG. 10(a), on the upstreamside, only a part of the blade cross section appears in the crosssection in the radial direction. Consequently, the air current leakseasily from the blade. As illustrated in FIG. 10(b) illustrating thecross section in the radial direction taken along the line X-X, in thecase where a pair of blades adjacent to each other relatively on frontand back sides in the rotation direction is focused for convenience sakeof description, an air current 18 a having leaked to the radially innerside after flowing into a blade 3 a on a forward side can be trappedagain with a blade 3 b on a backward side, which is adjacent to theblade 3 a, and thus an opportunity for increasing a pressure again isobtained.

On the other hand, an air current 18 b having leaked to the radiallyouter side cannot be trapped with the adjacent blade 3 b, and hence apressure cannot be increased. Therefore, it is important to hold the aircurrent flowing along the blade surface on the leading edge side(upstream side) so that the air current does not leak to the outer side.

In the second embodiment, as illustrated in FIGS. 8 and 9, the outerperipheral end tangent angle θ is kept constant from the leading edgeportion T0 to the point T1 on the way to the downstream side so that theair current does not leak to the radially outer side, and thus theenergy is supplied to the air current without fail.

Note that, the angle θ from the point T1 that is the terminal of theconstant value θ1 to the trailing edge portion T3 may also decrease in asmooth curved line as indicated by a broken line instead of decreasingin a straight line as illustrated in FIG. 8. For example, in the casewhere an increase in pressure required by the fan is large, a pressuredifference between the pressure surface and the negative pressuresurface increases, and hence the formed angle is decreased gently so asto prevent the leakage of the air current. On the contrary, in the casewhere the pressure difference is small, the angle θ may be decreasedmore rapidly compared to the above-mentioned solid-line embodiment so asto push out the air current to the downstream side. It is appropriatethat the angle be decreased so as to be suited to the environment inwhich the fan is used.

In the same way as in the first embodiment, even in the above-mentionedsecond embodiment, the air-blowing rate can be increased and theoccurrence of the leakage and the generation of a vortex can besuppressed more efficiently while achieving lower noise.

Third Embodiment

Next, a third embodiment of the present invention is described withreference to FIGS. 11 and 12. FIGS. 11 and 12 are views illustrating thethird embodiment respectively corresponding to FIGS. 8 and 9. A point T4of FIG. 11 is a corresponding point of an overlap starting point locatedat a position of the blade cross section including the above-mentionedoverlap starting point 10. In a propeller fan 201 according to the thirdembodiment, the outer peripheral end tangent angle θ takes a constantvalue from the leading edge point T0 to the corresponding point T4 ofthe overlap starting point and then decreases from the correspondingpoint T4 to the trailing edge portion T3. In the illustrated example ofFIG. 11, the outer peripheral end tangent angle θ decreases linearly.

A description is made regarding the foregoing. First, the outerperiphery of the propeller fan 201 is kept open in a space from theleading edge portion T1 to the corresponding point T4 of the overlapstarting point that overlaps the bellmouth, and hence the air currentleaks easily to the outer side. Therefore, the outer peripheral endtangent angle θ is kept constant from the leading edge portion T1 to thecorresponding point T4 of the overlap starting point so as to suppressthe leakage of the air current. Then, the outer peripheral end tangentangle θ is decreased to θ2 and θ3 respectively from the correspondingpoint T4 of the overlap starting point to the point T2 and the trailingedge portion T3 on the downstream side. Note that, the process ofdecreasing the angle is the same as that in the above-mentioned secondembodiment.

Also in the third embodiment, the same advantages as those in the secondembodiment are obtained, and further, in the third embodiment, inparticular, the effect of suppressing the leakage in the open region ofthe propeller fan 201 efficiently can be obtained.

Fourth Embodiment

Next, a fourth embodiment of the present invention is described withreference to FIG. 13. FIG. 13 is a radial sectional view of a blade of apropeller fan according to the fourth embodiment. As illustrated in FIG.13, in a propeller fan 301 according to the fourth embodiment, an outerperipheral bending portion 15 that bulges toward the downstream side isformed in an outer peripheral portion of the blade 3 with respect to thebending portion 13. Note that, in the fourth embodiment, the outerperipheral end tangent angle θ is also the same as any of theabove-mentioned first to third embodiments.

According to the fourth embodiment, the pressure difference between apressure surface lie and a negative pressure surface 12 a in a vicinity15 a of an outer peripheral edge at the outer side with respect to theouter peripheral bending portion 15 is reduced so as to weaken a vortex(blade tip vortex 16) generated due to the leakage of the air currentfrom the outer peripheral portion. Thus, compared to the above-mentionedembodiments of suppressing the leakage of the air current, in the fourthembodiment, the outer peripheral bending portion 15 is used in additionso that the air current can be prevented from generating a strong vortexeven in the case of the leakage of the air current, and thus thedisturbance of the air current in the case of the leakage thereof isminimized to further reduce the disturbance of the air current that iscaused by the vortex, thereby achieving lower noise.

Also in the fourth embodiment, the same advantages as those of the firstembodiment are obtained, and further, in the fourth embodiment, the aircurrent is prevented from generating a strong vortex even in the case ofthe leakage of the air current, considering also the state after the aircurrent leaks, thereby being capable of achieving still lower noise.

Fifth Embodiment

Next, a fifth embodiment of the present invention is described. As thefifth embodiment, the specific application of the above-mentionedpropeller fans is described. The propeller fans according to theabove-mentioned embodiments relate to the higher efficiency and thelower noise of the propeller fans. When the propeller fans are mountedon air blowers, highly efficient air blowing and an increase inair-blowing rate can be achieved. When the propeller fans are mounted onair conditioners and hot-water supply outdoor units, which arerefrigerating cycle devices including compressors and heat exchangers,the amount of an air current passing through the heat exchanger can beincreased also due to the highly efficient air blowing, and hence theenergy saving of the devices can be realized. Note that, in any of theair blowers, air conditioners, and hot-water supply outdoor units, thereis no particular limit to the configurations other than those of thepropeller fans, and for example, well-known and existing configurationsmay be used.

Although the details of the present invention are specifically describedabove with reference to the preferred embodiments, it is apparent thatpersons skilled in the art may adopt various modifications based on thebasic technical concepts and teachings of the present invention.

REFERENCE SIGNS LIST

1 propeller fan, 2 boss, 3 blade, 9 bellmouth, 10 overlap startingpoint, 10 a imaginary plane, 13 bending portion, 15 outer peripheralbending portion, O rotation axis, P apex, Q outer peripheral end, LQtangent, θ outer peripheral end tangent angle

The invention claimed is:
 1. A propeller fan, comprising: a rotatableboss; a plurality of blades formed on an outer periphery of the boss;and a bellmouth arranged so as to surround the plurality of blades at atrailing edge side of each of the blades, the blade including a bendingportion that bulges toward an upstream side in a cross-sectional shapein a radial direction, and wherein, in a blade cross-sectional view,assuming that a tangent at an end of the outer periphery is defined asLQ, an imaginary line orthogonal to a rotation axis O is defined as LO,an angle formed by the tangent LQ and the imaginary line LO is definedas an outer peripheral end tangent angle θ, and a position at which animaginary plane including a position of an intake-side end portion ofthe bellmouth and a peripheral edge of the blade cross each other isdefined as an overlap starting point, the outer peripheral end tangentangle θ on a trailing edge portion side with respect to a blade crosssection including the overlap starting point is smaller than the outerperipheral end tangent angle θ on a leading edge portion side withrespect to the blade cross section including the overlap starting point.2. The propeller fan according to claim 1, wherein the outer peripheralend tangent angle θ is constant between the leading edge portion and anarbitrary point on a backward side of the leading edge portion anddecreases between the arbitrary point and the trailing edge portion. 3.The propeller fan according to claim 2, wherein the arbitrary point islocated on the blade cross section including the overlap starting point.4. The propeller fan according to claim 1, wherein the blade comprises,in an outer peripheral portion with respect to the bending portion, anouter peripheral bending portion that bulges toward a downstream side.5. The propeller fan according to claim 1, wherein the blade comprises aswept blade including an outer side edge positioned on the downstreamside of the rotation axis with respect to a base on the boss side in across section in the radial direction.
 6. An air blower, comprising thepropeller fan according to claim
 1. 7. An air conditioner, comprisingthe propeller fan according to claim
 1. 8. An outdoor unit for ahot-water supply device, comprising the propeller fan according toclaim
 1. 9. An outdoor unit, comprising the propeller fan according toclaim
 1. 10. The propeller fan according to claim 1, further comprisinga connecting portion that gradually extends from the outer periphery ofthe boss to the bending portion without having a negative slope withrespect to the upstream side of the blade.